Dick Jordan, communications director for the Indianapolis-based United States Auto Club (USAC), calls the 500 the closest thing American auto racing has to a national convention. ''It's the gathering of the clan, so to speak, for all different forms of motor sports.''

Only a fraction of the sport's huge fan base will make it to the Speedway, but numerous other races, big and small, fall on the holiday weekend. The most significant of these is stock-car racing's Coca-Cola 600 in Charlotte, N.C., the world's longest oval-course event.

In Lakeville, Conn., sports cars will rev their engines at Lime Rock Park, one of America's premier road courses. Overseas, Formula One racers will join the auto-racing crescendo as they zip through the streets of Monte Carlo during the annual Monaco Grand Prix.

Americans, of course, have historically had a strong attachment to cars. Space-age automotive trends, however, have begun distancing many people from understanding the vehicles they drive. ''What you're looking at is a whole new motoring public that can't pop the hood open,'' says USAC's Jordan.

How this might ultimately affect auto-racing's popularity is hard to say. Clearly, though, race cars like those at Indianapolis have become incredibly sophisticated.

It shows in the attention required to maintain them at peak performance levels, says Brock Yates, a senior editor of Car and Driver magazine and a veteran racing writer. The annual budget for maintaining an Indy car can run between $10 million and $15 million, he says, and racing teams of 70 to 100 people, including engineers, designers, and computer technicians, are not uncommon.

''The old days of 'stab it and steer it' are gone,'' Yates says. ''At 225 m.p.h., incremental, micrometer-level adjustments to a wing angle or a suspension setting can be very important.''

Tiny misjudgments can prevent cars from even qualifying for high-tech races like Indy. It was just such a miscalculation, Yates believes, that accounts for the absence of the Penske racing team from Sunday's race.

Although a dominant team in recent years, not even skilled driving by Al Unser Jr. and Emerson Fittipaldi could make up for mechanical shortcomings. Defending-champion Unser will watch the fastest racing field ever (average speed: 226.912 m.p.h.) take off without him.